Tlshosts/FQDN.pem
tlshosts/FQDN.pem
man qmail-remote excerpt:
qmail-remote requires TLS authentication from servers for which this certificate exists (FQDN is the fully-qualified domain name of the server). One of the dNSName or the CommonName attributes have to match.
WARNING: this option may cause mail to be delayed, bounced, doublebounced, or lost.